A tool that punctures a living body with a needle is used to inject a liquid medicine into the living body, or extract a body fluid of the living body. When the needle attached to such a tool has a large external diameter, it is said that large pain is caused because a resistance force from the living body increases. For this reason, painless needles have been developed with the external diameter of the needles formed as thin as possible in order to reduce the pain.
In this case, because the needles formed in a thin shape have a small internal diameter, for example, the needles have a large flow resistance during injection of a liquid medicine into the living body. For this reason, a tapered needle has been presented (see Patent Literature 1). The tapered needle has a needle proximal portion having a diameter larger than the diameter of a needle distal portion, to reduce the flow resistance.
For example, the conventional tapered painless needles are formed with a thin external diameter, by rolling up a stainless plate material or elongating a stainless cylindrical member. However, in the case of a needle formed by rolling up a plate material, the joined portion of the rolled plate material needs to be processed with high accuracy. In addition, in the case of a needle formed by elongating a cylindrical member, rust due to the elongation may occur on the internal peripheral surface, and therefore the processing is very difficult. Accordingly, manufacturing of these needles requires much time and great cost.
To solve the above problems, a method for forming a needle by electroforming has been presented (Patent Literatures 2 and 3). In the method, a core material having a diameter corresponding to a passage of the needle is immersed in an electrolyte, an electroformed member is formed on an external peripheral surface of the core material, thereafter the core material is pulled out of the electroformed member, and an end portion of the electroformed member is ground to have an acute angle.